Abstract: To explore the temporal variations of the rates of soil respiration and its components in the burned area of plantation forests in coastal regions and related influencing factors, we measured soil respiration in the burned area of Eucalyptus urophylla ×Eucalyptus grandis plantation in coastal sandy land of Fujian Province by the Li-8100 carbon flux automatic measurement system. Soil heterotrophic and autotrophic respirations were distinguished by the trench method. Soil temperature (T₁₀) and soil volumetric water content (W₁₀) at a depth of 0-10 cm were measured. The monthly variations of soil respiration and its components and hydrothermal factors were analyzed in the burnt and control plots. The correlations between soil respiration rate and soil temperature, soil moisture, and soil physicochemical properties were analyzed. The results showed that the monthly average rates of soil total respiration, heterotrophic respiration, and autotrophic respiration were 2.20, 1.87, 0.33 μmol·m^-2·s^-1 in the burned plots, and were 2.96, 2.15, 0.81 μmol·m^-2·s^-1 in the control plots, indicating that soil respiration and its components in the burned plots were significantly decreased (P<0.05). Soil respiration and its components in the burnt and control plots had significant exponential correlation with T₁₀, while the total respiration rate in the burnt and control plots showed a significant positive correlation with W₁₀. There was no significant correlation between heterotrophic respiration and W₁₀ in the burnt plots, while soil heterotrophic respiration in the control plots showed significant positive correlation with W₁₀. The Q₁₀ values of soil total respiration and heterotrophic respiration were the same in the burned plots, being slightly lower than that in the control plots. Soil respiration rate was positively correlated with soil NO₃^--N, inorganic N, and NH₄⁺-N. In E. urophylla ×E. grandis plantation, forest fire significantly affected soil respiration rate by reducing soil heterotrophic and autotrophic respiration. According to the results of regression model, soil total respiration was significantly correlated with soil temperature and volumetric water content, indicating that soil temperature and water content are the main factors affecting the respiration rate of forest soil. Furthermore, forest fire can change soil carbon and nitrogen components, thereby affecting soil carbon emission rate.

Key words: coastal sandy land, mild fire, autotrophic respiration, heterotrophic respiration, temperature sensitivity index.